The context for the first 3 was all related to a question about what would happen if you played Copper during Black Market action, then later played a Coppersmith. People were wondering if the already-played Copper would get the bonus. Of course it doesn't.
Can I get clarification on this statement? Sure, if you had spent the copper you played in the black market action then it wouldn't get the bonus, but if it is unspent...Coppersmith doesn't say that coppers played after it produce +1coin, it says that copper in general produce +1coin. So why wouldn't a copper played during the black market action (but unspent) be worth 2coin during your buy phase?
The amount Copper produces only matters at the moment you play the Copper. The Coppers played earlier in the turn would now produce $2, if only you played them, but you aren't playing them, you played them already, and when you played them they just made $1.
Playing treasures gives you coins to spend, just like playing actions that produce coins. You spend the coins rather than the treasures; the treasures are out of the picture. Normally this distinction is less visible, because you play your treasures and immediately spend the money or don't.
